1. Field of the Invention
The present invention relates to web handing apparatus and to a method for web handling. More particularly, the present invention relates to web handling apparatus and a web handling method wherein the speed of movement of a downstream portion of a moving web of material is varied while the upstream portion of the web that approaches the web handling apparatus is maintained at a constant web speed.
2. Description of the Related Art
It is often desirable in various manufacturing operations to control the speed of a moving web of material to temporarily change the speed of the web in response to a particular operating condition, or to enable the performance on the web of a particular operation. In that regard, the web speed can be changed in a number of ways, including varying the speeds of intermediate feed rolls that guide the web along, sometimes with web storage apparatus such as dancer rolls, shuttle devices that reciprocate to temporarily shift the web, or the like. Alternatively, the speed of a moving web can be changed by varying the speed of a drive motor that drives an unwind stand or a web take-up roll that causes web movement through the web handling apparatus.
Although web-speed-change devices are known, the use of such known devices often involves web speed changes that are achieved by periodically accelerating and decelerating various of the rotating elements of the web feed system. As a result, varying cyclic loads are imposed on the respective rotating elements of the web feed apparatus, and those varying loads cause varying levels of cyclic stress on those elements. The varying stress levels, which also are influenced by the magnitude of the output and speed of the drive motor, can, over time, lead to the need for more frequent maintenance and replacement of parts because of increased wear that occurs as a result of the changing stress levels. Additionally, to periodically accelerate rotating elements to effect web speed changes requires a larger size, more costly drive motor that provides a higher output power than would be required if the rotational speeds of the rotating elements were maintained substantially constant.
Accordingly, it is desirable to provide apparatus that allows the speed of a web to be controlled to a desired value at a particular point in a manufacturing process, either greater than or less than the speed of the incoming web, while maintaining the incoming web speed at a constant value. Consequently, rotational speed changes within the web feed mechanism are desirably avoided, to minimize the stresses on and the resulting wear of the rotating elements of the apparatus, and to reduce the need for frequent servicing and repair of rotating elements of the apparatus.
It is also desirable to eliminate the need for reciprocating web-take-up devices, such as dancer rolls and shuttles that are sometimes employed in web feed devices to allow changes of web output speed while maintaining the web input speed substantially constant. An example of one such reciprocating, shuttle-type device is disclosed in U.S. Pat. No. 5,693,165, entitled xe2x80x9cMethod and Apparatus for Manufacturing an Absorbent Article,xe2x80x9d which was issued on Dec. 2, 1997, to Christoph Schmitz.
Another proposal for periodically changing the speed of a web while the web infeed speed is maintained constant is disclosed in U.S. Pat. No. 5,407,513, entitled xe2x80x9cApparatus and Process for Cyclically Accelerating and Decelerating a Strip of Material,xe2x80x9d which issued on Apr. 18, 1995, to Michael P. Hayden et al. The apparatus disclosed in that patent includes an eccentric accelerator in the form of a spindle that is carried on a rotating drive shaft and that is offset from the axis of rotation of the drive shaft. Accordingly, as the drive shaft rotates the periphery of the spindle describes a circle that is concentric with the axis of the drive shaft. The apparatus disclosed in that patent is utilized in the context of apparatus for changing the speed of a web of a fastener material that is to be applied at spaced intervals to a second moving web. Because of the spacing of the fasteners that are cut from the web of fastener material, the incoming speed of the fastener material is maintained constant while the web passes over the eccentric accelerator to periodically accelerate and decelerate the web of fastener material to enable a cut to be made so that the cut portions are properly positioned relative to a base sheet with which the cut portions are associated. However, in that apparatus the cut that is made in the web is a transverse cut that extends perpendicularly to the web movement direction, and the eccentric accelerator causes the fastener web to only instantaneously match its speed with that of a cutter and anvil roll combination that effects the transverse cuts in the fastener material. As a result, the Hayden et al. device does not permit cuts to be made that are at an angle with the web movement direction and that take place over a given period of time, as opposed to instantaneously.
An object of the present invention to provide a method and an apparatus that allows a constant web infeed speed with varying web output speeds, and that will enable an angular cut to be made in the web material by matching the web speed to the surface speed of a downstream operation for a predetermined time period.
It is another object of the present invention to provide a web feed system for changing a web output speed while maintaining web input speed constant and while maintaining at a substantially constant value the rotational speeds of the rotating elements of the system.
In accordance with one aspect of the present invention, a web speed metering apparatus is provided for receiving and engaging a web that is supplied to the metering apparatus at a constant in-feed speed. The output speed of the web leaving the metering apparatus is cyclically varied. The apparatus includes a rotatable shaft that defines an axis of rotation and that is disposed across a path of movement of a web of material to be metered. An elongated, web-engaging surfaces is carried on the shaft and extends axially thereof to define a surface having a constant cross-sectional configuration in a direction perpendicular to the axis of rotation. The web-engaging surface is adapted to receive an incoming web that travels at a constant in-feed speed and defines a non-circular cross-section in a direction perpendicular to the axis of rotation. The cross-section has a centroid that is offset from the axis of rotation to cause the output speed of the web as the web leaves the web-engaging surface to vary as a function of the instantaneous radial spacing of the web from the axis of rotation of the web-engaging surface.
In accordance with a further aspect of the present invention, a method is provided for varying the output speed of a first moving web having a constant input speed and a timed relationship with a web processing station for a continuously moving second web that is supplied at a constant in-feed speed. The method includes the steps of feeding the first moving web at a first constant speed to a web deflection station for a predetermined first time period to allow an operation to be performed on the web downstream of the deflection station. An intermediate portion of the moving web is deflected so that the speed of the leading edge of web is decreased for a predetermined second time period to a speed less than that of the first constant speed to allow a predetermined leading edge advancement length. Deflection of the moving web is terminated and the leading edge of the web is fed at the first constant speed for the predetermined first time period. The leading edge of the moving web is advanced at predetermined distance and is fed at the first constant speed for the predetermined first time period.